110 MEXICO AND CENTRAL AMERICA 
the sun, and that it appears much smaller, because 
farther from the earth, when near the superior con- 
junction. Moreover, we must expect beliefs as to the 
nature of this planet, personified as a god, to supple- 
ment the knowledge gained from actual observations. 
The agreement in length between 8 solar years of 
365 days each and 5 Venus years of 584 days each was 
recognized and used in ceremonies and calculations. On 
the five pages of the Dresden Codex, numbered 46-50, 
is presented a series of 5 Venus years amounting in all to 
2920 days. On page 24 (see Pl. XX) of the same codex 
we find this sum taken 13 times to make 37,960 days and 
then this last number taken 4 times to make 151,840 
days. The number 2920 (5 x 584 and 8 x 365) has a 
definite relation to the tonalamatl which results from 
the following coincidence: 260 and 584 have a com- 
mon factor of 4. It therefore follows that when groups 
of 584 days are counted consecutively along with the 
twenty named days in the standard tonalamatl, these 
groups of 584 days can begin on only five different days. 
The sixth period is introduced by the same named day 
as the first but this named day is associated with a 
different number. The same named day combined 
with the same number recurs in 13x2920 or 37,960 days. 
This round of the Venus calendar (65 Venus years of 
584 days and 104 solar years of 365 days) equals exactly 
two rounds of the solar calendar. 
But there is an important correction that has to 
be made to keep the actual solar calendar in accord 
with the actual Venus calendar. ‘The solar year is really 
365.24 days in length and we have seen that this error 
was corrected by a marginal addition of 25 days in 104 
years. The mean Venus year is really 583.92 or .08 of a 
day less than 584. The actual position of Venus will 
therefore run ahead of its calendrical position and there 
